The present invention relates to a method for manufacturing a heat insulating sash bar for window sash or, more particularly, to a method for manufacturing a heat insulating sash bar of which remarkably improved heat insulation is obtained between the face plates of the sash bar, one facing the inside of the room and the other facing the outside of the room, as connected with connecting members of a heat insulating material in such a manner as to form a hollow space surrounded by the face plates and the heat insulating connecting members.
As is well known, many of the modern window sashes are framed with sash bars made of a metal such as aluminum and shaped by extruding in the form of bar materials. When such window sashes are to be used in severe climatic conditions, there may be a problem in the use of an integrally shaped metal-made sash bar in respect of the heat insulation between inside and outside of the room since the heat conduction through the integrally shaped sash bars is not negligibly small due to the high heat conductivity of aluminum or the like metal of which the sash bar is made.
In this connection, it is desirable that the two oppositely positioned face plates forming the sash bar, one facing the inside of the room and the other facing the outside of the room, are not integral by isolated thermally from each other with connecting members made of a heat insulating material. In the prior art, various methods have been proposed for manufacturing such a heat insulating sash bar. For example, an integral bar material having an approximately H-wise cross section, composed of two oppositely facing face members connected with an inner connecting part to form at least one groove-like channel one one side of the connecting part, is shaped by extrusion and the groove-like channel is filled with a pourable heat insulating material to be cured in situ followed by longitudinally removing at least part of the connecting part by cutting off by use of a cutter or by tearing off at the reverse side of the heat insulating material to thermally isolate the two oppositely positioned face members.
In the above described conventional method for manufacturing a heat insulating sash bar, it is sometimes unavoidable that the heat insulating material which has been cured in contact with the inner connecting part, is more or less shaved off by the blade of the cutter when the cutter blade is thrusted into the connecting part and the thus formed shaving dusts electrostatically charged during the cutting work adhere to the outer surface of the bar material. Therefore, such adhering dusts of the heat insulating material must be removed with great consumption of time and labor. In addition, shaving of the heat insulating material with the cutter blade may cause cracking or fissures in the heat insulating material resulting in decrease of the connecting strength between the face members through the heat insulating material as the connecting member.
In order to avoid thrusting of the cutter blade into the heat insulating material, two parallel incision lines are formed on the connecting part and the portion between the incision lines is removd by tearing off. This method of tearing off is also not free from the problem caused by the adhesive bonding between the heat insulating material and the connecting part to be removed.
A further problem in the above described conventional method is that, since the surface of the section formed by the removal of part of the connecting part by cutting or tearing off is exposed bare to the outer atmosphere, corrosion of the metal sash bar readily starts at this surface of section by the influence of the atmospheric moisture because the surface of section is not provided with any surface protective layer different from the other surfaces of the bar material provided in advance with a protective coating layer formed, for example, by anodic oxidation.
A remedy for the above problem of the exposed surface of section is disclosed in Japanese Patent Publication No. 56-1434 in which a second impregnation with the heat insulating material is undertaken to cover the surface of section after a part of the connecting part has been removed by cutting off. This method is indeed effective in protecting the surface of section from cor-rosion but the other problems described above are left unsolved. Furthermore, the second impregnation with the pourable heat insulating material in this method is performed at the side of the connecting part reverse to the first impregnation with the heat insulating material so that no hollow space can be retained with the bar material. Therefore, an extremely large volume of the heat insulating material is used to fill up the space within the bar material resulting in disadvantages not only due to the economical problem by the large costs for the heat insulating material but also due to the difficulty in manufacturing and handling by the excessively heavy weight of the sash bar, especially, when the sash bar is large in the face measure.